experiments with semifluxon generator
DESCRIPTION
Experiments with semifluxon generator. Edward Goldobin University of Tübingen, Germany M. Paramonov, M. Fominsky, V. Koshelets IRE RAS, Moscow. [Logo of МОН 1.5 here]. Where is Tübingen?. Tübingen : small university town on r. Neckar population ~80000 - PowerPoint PPT PresentationTRANSCRIPT
Experiments withsemifluxon generator
Edward GoldobinUniversity of Tübingen, Germany
M. Paramonov, M. Fominsky, V. KosheletsIRE RAS, Moscow
[Logo of МОН 1.5 here]
Where is Tübingen?
Tübingen
Tübingen:• small university town on r. Neckar• population ~80000• 30 km south from Stuttgart
-- a capital of Baden-Württemberg
University:• students ~28000• university is 530 years old !!!• two faculties of theology ;-)• strong medicine• phys., chem., math are small
Our Group (~30 people):• 2 Profs: R. Kleiner, D. Koelle• 1 Assistant Prof.• 4 Post Docs• ~12 PhD students• ~10 Diploma students
Josephson junction
Conventional JJ. (0-junction)
Unconventional JJ (-junction)SIS
SIS
I
I
+other terms
jc=1–5000 A/cm2, (Nb-AlOx-Nb)0 1 2 3 4 5 6
-1.0
-0.5
0.0
0.5
1.0
sup
erc
urr
en
t
phase
11
is en
22
is en
12 :phase Josephson
11
is en
22
is en
Long Josephson 0- junction
0 x
1D model
YBCO-Nb ramp zigzags
H.-J. Smilde at al. PRL 88, 57004 (2002)
LTSEM image of supercurrent
E. Goldobin, R. Straub, D. Dönitz,D. Koelle, R. Kleiner,H. Hilgenkamp (2003).
SFS/SIFS junctions
V. Ryazanov et al. PRL 86, 2427 (2001)
T. Kontos et al. PRL 89, 137007 (2002)
sine-Gordon equation for 0- LJJ
Phase discontinuity points!
Goldobin et al., PRB 66, 100508 (2002)
— dimensionless damping
— the first critical field
— dimensionless field
Semifluxon=vortex carrying
-3 -2 -1 0 1 2 3 -3 -2 -1 0 1 2 3
0.0
0.5
1.0
1.5
2.0
-3 -2 -1 0 1 2 3
-1.0
-0.5
0.0
0.5
1.0
fluxo
n
(x)
2
2
coordinate x
phas
e
(x) (a)
coordinate x
2
x(x)
mag
netic
fie
ld
(b)
fluxon
sem
i-flu
xon
semi-fluxon
fluxo
n
coordinate x
supe
rcur
rent
(c)
Pinned, two degenerate states and
Goldobin et al., PRB 66, 100508 (2002)
Xu et al., PRB 51, 11958 (1995)
Mechanical analog:pendula chain
(x)
(x)
Semifluxons observation
SQUID microscopy on YBCO-Nb ramp zigzag LJJs
H. Hilgenkamp et al. Nature 422, 50 (2003).
Artificial 0- junctions
Goldobin et al., Phys. Rev. Lett. 92, 057005 (2002)
A. Ustinov, Appl. Phys. Lett. 80, 3153 (2000).
Nb LJJ with two injectors
J 30 m (jc 100 A/cm2)
Calibration of injectors
Numerical Experimental
-2 - 0 + +20.0
0.2
0.4
0.6
0.8
1.0
criti
cal c
urre
nt c
phase discontinuity -40 -30 -20 -10 0 10 20 30 40
0.00
0.05
0.10
0.15
0.20
0.25
0.30
I inj =
+0.
3 m
A
I inj =
+13
.5 m
A
criti
cal c
urre
nt I
c (m
A)
current through injectors Iinj (mA)
I inj =
–12
.8 m
A
Goldobin et al., PRL 92, 057005 (2004)
Switching on the current...
at zero bias we have a static pinned semifluxon. bias current pulls semifluxons, just like fluxons. but semifluxons are pinned --> deformation at bias=Ic0.64 Ic switching to the R-state
Goldobin et al., PRB 67, 224515 (2003).
mag
netic
fie
ld
Overcritical bias:oscillator
Frequency depends on: bias current, damping, length two outputs shifted by 180° more stable than flux-flow due
to semifluxon pinning
volta
ge
0.0
0.5
1.0
1.5
2.0
0 1 2 3 4 5 6 7
L=40J
L=20J
L=10J
normalized voltage u
bias
cur
rent
N. Lazarides, PRB 69, 212501 (2004).
-3 -2 -1 0 1 2 3
-1
0
1
coordinate x
mag
netic
fie
ld (
a.u.
)
Semifluxon -- half-integer ZFS
Finite length --> image technique: 1 real semifluxon + 2 anti-semifluxons (images)
Bias current Force SF hopping.
Goldobin et al., Phys. Rev. B 67, 224515 (2003).
Half integer ZFS (full IVC)
0,0 0,5 1,0 1,5 2,0 2,5 3,0
0,0
0,1
0,2
0,3
0,4
0,5
semi-integer ZFS
bi
as c
urre
nt,
mA
voltage across LJJ, mV
integer ZFS
Goldobin et al., PRL 92, 057005 (2004)
Half integer ZFS
0 100 200 300 400
0
20
40
60
80
sem
i-in
tege
r Z
FS
bias
cur
rent
(A
)
voltage across LJJ (V)
inte
ger
ZF
S
resonantstructures
Im
Goldobin et al., PRL 92, 057005 (2004)
Experiments last week in IRE
Layout
L = 16..32 mdx=dw=1, 1.5, 2 m
Calibration: Ic(ICL) & Ic(Iinj)
I-V characteristic of generator
SIS detector
Emission linesDifferent bias points along the semifluxon step
Autonomous linewidth ~1.2 … 10 MHz
And now with PLL ;-)
with PLL the spectral ratio is up to 97%
Summary & ProblemsSummary many samples work (both generator and detector) we observe expected operation: a semifluxon step, SIS pumping we have measured autonomous linewidth ..and linewidth with PLL
Outlook (problems & todos): maximum Ic in Ic(H) and Ic(Iinj) are not equal
in high freq. setup strange shunt resistance of ~3 Ohm in high freq. setup strange dep. of voltale on Iinj.
Repeat again with remaining 2 samples and try to make new ones. Compare linewidth with inj with the one with CL. Compare with ZFS not all LO freq were good